The Green party has backed the Liberal Democrat candidate in the Richmond Park byelection against former Conservative Zac Goldsmith, who quit his seat in protest at the government’s decision to expand Heathrow airport.

The party said they hoped the decision would put pressure on the local Labour party to not stand a candidate of their own and instead swing behind the Lib Dems as the best chance of beating Goldsmith, who is standing as an independent and has been endorsed by Ukip.

Andree Frieze, who was the Greens’ selected candidate for the seat, told her local party she was keen not to contest it, a decision agreed on Thursday night with Kingston Greens. “I believe, wholeheartedly, that I am the right person to do the right thing – for the people, for the planet,” she said.

“Realistically, however, I am not going to win and my standing could allow Zac, yet again, to be the wrong person representing our community. Furthermore, by not standing and helping a non-Tory win, we have the chance to seriously dent the Conservative majority.”

The Conservatives are not putting up their own candidate for the byelection on 1 December but Goldsmith has been endorsed by the local Tory party and supported by his neighbouring Conservative MP Tania Mathias.

The Liberal Democrats have already confirmed Sarah Olney, a local accountant who is also anti-Heathrow expansion, as their candidate to run against Goldsmith. The party, which held the seat until 2010, has put huge resources into winning it back and are pinning their hopes for victory on being able switch the conversation from Heathrow to Brexit in the pro-remain constituency.

Goldsmith, a keen environmentalist, voted to leave the EU. He was also widely criticised for his mayoral campaign, which opponents said used dog-whistle tactics against Labour’s Sadiq Khan.

Jonathan Bartley, the Greens’ co-leader, met local members of the Richmond Greens on Wednesday night, where the decision was taken to endorse Olney to boost parliamentary opposition to a hard Brexit. Kingston Greens also endorsed that decision at a meeting on Thursday.

“This is no normal byelection,” Bartley said. “A regressive alliance of the Tories and Ukip are working together to reinstall a pro-Brexit MP who ran a racist campaign to be mayor of London.

“The decision not to stand has been made because we believe that a win for a non-Conservative candidate would be a blow to the Tory’s hard Brexit and dent their damaging plans for post-referendum Britain. Ultimately we think Britain is better off without Zac Goldsmith returning to parliament.

“I’d now urge Labour to join us in forming a progressive alliance against the forces of Conservatism and narrow-mindedness.”

Chair of Richmond’s Greens, Richard Bennett, said local Liberal Democrats recognised that in the 2018 council elections the parties should work together in some wards “to ensure people get the best chance both of Green party representation and of a council not controlled by the Conservatives.”

Labour is determined it will contest the seat, however. Alice Perry, who is a Labour national executive committee member, said shortlisting interviews to choose the party’s candidate for Richmond Park had taken place this week and that the candidate will be formally selected by local party members from a shortlist on Saturday.

“We are definitely standing a candidate,” she said. “The Tory Lib-Dem coalition government made massive cuts to valued public services, including huge cuts to council budgets. The Lib Dems’ actions in government proved they are not a progressive party.”

Labour’s Sachin Patel, who fought the seat at the last general election, has already declared his intention to stand again.

Tim Farron, the Lib Dem leader, said his party had an environmental record that Green voters could support, including pushing for lower emissions targets, paving the way for the Paris agreement, renewables investment, the plastic-bag charge and opposition to airport expansion.

“You only have to compare that with the destructive Conservative Brexit government which is trying to force through Heathrow expansion, release polluters from tough EU environmental laws and slash subsidies for renewables, which has already led to 12,500 job losses in the solar industry alone,” he said.

“It is vital that progressive voters get behind the only credible progressive candidate, Sarah Olney.”

Lib Dems pull off shock victory in Richmond Park by-election as Zac is thrown out

A ‘shockwave to Downing Street’ has, last night, been pulled off by the Liberal Democrats, with Sarah Olney defeating Zac Goldsmith in the Richmond Park by-election.

Lib Dem challenger Ms Olney overturned Mr Goldsmith’s 23,015 majority to win by 1,872 votes. The result saw Ms Olney poll 20,510 votes to Mr Goldsmith’s 18,638, on a turnout of 41,367, or 53.6 per cent. The 21.74 per cent swing to the Lib Dems from Mr Goldsmith topped the 19.3 per cent swing the Lib Dems achieved from the Tories in the Witney by-election.

A Green Party spokesperson said: “The Green Party’s decision to stand down and the huge drop in the Labour Party vote show that people will vote tactically. It proves that there is a huge appetite and a need for proportional representation so that people can express a real preference at elections. In Sarah Olney, we now have an MP who will push for the electoral reform that we so urgently need. We look forward to working with the Liberal Democrats, Women’s Equality Party and the Labour Party in a Progressive Alliance for the 2018 local elections and the next General Election.”

Ms Olney said the shock victory was a rejection of the “Ukip vision” of Britain, and the politics of “anger and division”.

In her victory speech, she said: “The people of Richmond Park and North Kingston have sent a shockwave through this Conservative Brexit government, and our message is clear: we do not want a hard Brexit. We do not want to be pulled out of the single market, and we will not let intolerance, division and fear win.”

In a brief acknowledgement of the result, a clearly downcast Mr Goldsmith said: “This by-election that we have just had was not a political calculation, it was a promise that I made and it was a promise that I kept.”

Labour’s Christian Wolmar lost his deposit as he trailed a distant third with 1,515 votes, losing 8% of the Labour vote compared to 2015.

A Conservative Party spokesman said the result would make no difference to Brexit plans, stating: “This result doesn’t change anything. The Government remains committed to leaving the European Union and triggering Article 50 by the end of March next year. Commiserations to Zac Goldsmith on his defeat. We are sorry that he is no longer in the House of Commons.”

Lib Dem leader Tim Farron said: “The message is clear: The Liberal Democrats are back and we are carrying the torch for all of those who want a real opposition to this Conservative Brexit government.

“This was a remarkable, come-from-nowhere upset that will terrify the Conservatives. A year and a half ago, their man won by nearly 40% and had a majority of more than 20,000. In one fell swoop we have wiped that out completely.

“If this was a general election, this swing would mean the Conservatives would lose dozens of seats to the Liberal Democrats – and their majority with it.

Mr Wolmar said voters had disliked Mr Goldsmith’s “ghastly, disgusting” bid to be London Mayor in which Labour accused him of running a racist campaign against Sadiq Khan.